Leptospirosis is the designation for a group of zoonoses caused by the bacteria Leptospira interrogans which is related to spirochetes (4). The name reflects the bacterium’s appearance: Leptos means narrow or fine, while speira is the Greek word for spiral. The incubation period of leptospirosis is 2 – 20 days, and in most cases the infection has a subclinical or mild, influenza-like course. Fever, headache and myalgia are common symptoms, while abdominal pain, conjunctivitis and exanthema occur less frequently. In septic courses, affection of the liver and kidney, meningitis or encephalitis, myocarditis and pulmonary symptoms such as coughing and dyspnoea are also seen. The septic phase may last for up to a week. Without treatment, the fever often abates after a week, but some patients have relapses of fever for a further 1 – 2 weeks. Some of the organic symptoms of the disease are probably due to immunological responses to the infection. In serious courses, thrombocytopaenia, leukocytosis with neutrophilia, icterus and microscopic haematuria are common (3). Hypokalaemia and hyponatraemia are often seen and are probably due to the ability of the bacteria to inhibit active Na-K-Cl co-transport in the ascending limb of Henle’s loop in the kidneys (5, 6). Electrolyte imbalances may be exacerbated by diarrhoea and renal failure. Mortality for serious leptospirosis is about 10 %, even with appropriate antibiotic treatment (3, 7).
Although the combination of travel history, symptoms and clinical findings may give rise to suspicion of leptospirosis, a number of other infectious diseases are also possible differential diagnoses. Milder forms of leptospirosis can be confused with influenza or similar viral infections. In our case history, nephropathia epidemica was a possible differential diagnosis, while human granulocytary ehrlichiosis and rickettsioses were far less probable. The clinical findings in cases of dengue fever are also sometimes similar to leptospirosis, but a short incubation period and the travel destination excluded this disease in our patient. Because of elevated liver values, viral hepatitis was another possibility. With heptatitis A in particular there is fever and muscular aching in the preicteric phase.
In this case, however, the patient’s travel account was typical and the disease picture classical for severe leptospirosis ? Weil’s disease ? and the diagnosis was confirmed by positive serology. A serological test is the most important means of diagnosing leptospirosis. In Norway, leptospirosis serology is performed at the Norwegian Institute of Public Health. The test used there detects both IgM and IgG. The sensitivity and specificity are over 95 %, and the positive predictive value for identification of acute leptospirosis is 90 % (8). Leptospirosis can also be diagnosed by detecting the bacteria in cultures of blood, urine, spinal fluid or other bodily fluids on a special medium. In the acute septic phase in particular Leptospira can be detected in blood. As culturing usually requires a special medium, the referral to the laboratory must indicate that Leptospira is suspected. The bacteria grow slowly, and it may be several weeks before they can be detected in a culture (3). In our patient, Leptospira was not found in cultures of urine or blood taken at the time of admission. This may be because culturing on a special medium was not requested, or because the microbe was no longer present in the patient’s blood or urine.
When it comes to treatment, there is not an adequate scientific knowledge base for setting clear guidelines for the choice of antibiotic. Penicillin, ampicillin, doxycycline and ceftriaxone all appear to be effective as long as treatment starts early in the course (9). If leptospirosis had been suspected at the time of admission of our patient, a narrow-spectrum antibiotic with less potential for developing resistance, such as penicillin, would probably have been the first choice. But treatment with ceftriaxone also caused a rapid improvement in his condition.
In Norway, leptospirosis is primarily an imported disease affecting persons who have been in contact with fresh water contaminated with infected animal urine. The bacteria can survive for several months in water and moist soil. They can penetrate skin or be transmitted if contaminated water is swallowed or comes into contact with wounds, for example during bathing, rowing and other water sports. Rats are probably the most frequent source of infection, but dogs, pigs, cattle, horses and hedgehogs may also be reservoirs for some serotypes (4). Men appear to be more susceptible to infection than women (10). The bacteria occur worldwide, but most frequently in tropical areas (3). However, leptospirosis has been detected in dogs in Norway in recent years, a sign that the bacteria also occur in this country (4). Since detection requires a special medium and tests are seldom performed unless there is suspicion of an imported disease, it is possible that there are also undiagnosed cases of the disease in Norway. If antibiotics that are often administered in the case of unclear infection conditions are effective, this may also lead to the prevalence being underestimated.
So the patient’s relative (and the department’s infectious diseases doctors) were right. Our patient was probably infected while rowing on fresh water in southern France 1 – 2 weeks before his admission, and the wound on his right elbow may have been the port of entry for the microbe. When the disease is less acute, it is more difficult to make a diagnosis. In cases of serious influenza-like symptoms in persons who have been exposed to fresh water in endemic areas in recent days or weeks, tests should be taken with leptospirosis in mind, and treatment started if there is suspicion of leptospirosis.